Invisible indicia printed with an optically active material on a reflective substrate can be used as a covert security feature on products and product packaging. The product is authenticated by revealing the invisible indicia with the use of a circular polarizing filter. The circular polarizing filter is held in close proximity to the printing. The person holding the filter can then authenticate the item by visually verifying the image or human-readable text or code that is revealed as expected. While this can be an effective security feature, the authentication process has limitations.
When authenticating product out in the field, it is often the case that many items need to be authenticated sequentially, and the results of the authentication audit need to be transmitted to another location. It is therefore useful to be able to automate the method for recording and storing the results and to have a convenient means of transmitting the results once collected.
It is sometimes desirable to have an immediate response to a positive or negative authentication audit. It is therefore useful to have a system that can not only transmit the results of an authentication audit, but also then receive a response back.
It is also often desirable to encode a large amount of data in invisible indicia, for example an item-level serialized number. To reduce the amount of space required to print the data or to speed up reading the printed information, it can be printed in the form of a machine readable code rather than a human-readable code, for example a linear or 2-dimensional bar code. It is therefore useful to be able to quickly and conveniently decode a revealed machine-readable code to be able to quickly authenticate the item.
Finally, at times, it is very desirable for investigators to perform their audits in a covert manner, often without handling the item to be authenticated. It is therefore useful to be able to authenticate an item from some distance away and not to require the revealing device be in close proximity.